We are conducting a family interview study of homosexual and heterosexual orientation. Index subjects are unmarried men, age 25-35. Relatives sought are their brothers and sisters. For index subjects and relatives we determine sexual orientation, cognitive abilities (verbal and spatial), self-reported "masculinity-femininity", vocational interests, life history of mental disorder. We ask: Does a particular sexual orientation run in families? Do homosexual and heterosexual men (and their relatives) differ in cognitive abilities, interest patterns or history of mental disorder?